A gps receiver is disclosed wherein gps position measurement can be performed stably and rapidly without the necessity to wait for periodical time information from a gps satellite and power consumption is minimized also with a minimized position measurement time through the selection of an optimum time interval between intermittent receptions of gps signals. The gps receiver includes a gps block for performing position measurement based on a signal transmitted from a gps satellite to update a navigation message and repeating standby and startup thereof, an external clock block for holding frequency information and time information of a high accuracy and outputting a start signal to the gps block, which is in a standby state, based on the frequency information and the time information held therein, and a frequency measurement block for measuring a frequency offset which is a displacement of a frequency oscillator of the gps block with reference to the frequency information held in the external clock block and outputting information of the measured frequency offset to the external clock block.
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4. A gps receiver, comprising:
a gps block for receiving a signal transmitted from a gps satellite and performing position measurement based on the received signal to update a navigation message and for repeating a standby state for reception and a startup state thereof; and an external clock block for storing frequency information and time information of a high accuracy; said external clock block outputting a standby signal and a start signal, which are to be transmitted to said gps block, at predetermined time intervals based on a setting signal transmitted from said gps block and the frequency of information and the time information stored in said external clock block.
7. A gps receiver, comprising:
a gps block for receiving a signal transmitted from a gps satellite and performing position measurement based on the received signal to update a navigation message and for repeating a standby state for reception and a startup state thereof; and a radio wave clock block for holding time information of a high frequency and frequency information of a high accuracy obtained through reception of a signal transmitted from a radio wave clock broadcasting station; said radio wave clock block outputting a standby signal and a start signal, which are to be transmitted to said gps block, at predetermined time intervals based on a setting signal transmitted from said gps block and the time information and the frequency information stored in said radio wave clock block.
2. A gps receiver, comprising:
position measurement execution means including a frequency oscillator for performing position measurement based on a signal transmitted from a gps satellite; radio wave clock reception means for receiving a carrier from a radio wave clock broadcasting station; and frequency measurement means for measuring an error of said frequency oscillator of said position measurement execution means based on a frequency of the carrier received by said radio wave clock reception means, wherein said frequency measurement means outputs the measured error of said frequency oscillator to said radio wave clock reception means, and said radio wave clock reception means controls startup/standby of said position measurement execution means based on the error of said frequency oscillator outputted from said frequency measurement means.
1. A gps receiver, comprising:
a gps block for performing position measurement based on a signal transmitted from a gps satellite to update a navigation message; an external clock block for holding frequency information and time information of a high accuracy and outputting a start signal to said gps block, which is in a standby state, based on the frequency information and the time information held therein; and a frequency measurement block for measuring a frequency offset which is a displacement of a frequency oscillator of said gps block with reference to the frequency information held in said external clock block and outputting the measured frequency offset to said external clock block, wherein said external clock block controls standby and startup of said gps block based on the frequency offset outputted from said frequency measurement block.
3. A gps position measurement method for a gps receiver, comprising the step of:
receiving a hierarchical navigation message from each of a plurality of gps satellites; storing the received navigation messages into a memory; storing frequency information and time information of a high accuracy into an external clock which normally is in an operating state; and repeating startup and standby of said gps receiver within a predetermined time determined using the frequency information and the time information held in said external clock to perform position measurement of said gps receiver from said gps satellites to update the navigation messages stored in said memory, wherein an interval of time between startup and standby of said gps receiver is varied based on a degree of accuracy of the frequency information or the time information held by said external clock.
9. A gps position measurement method for a gps receiver, comprising the steps of:
receiving a hierarchical navigation message from each of a plurality,of gps satellites; storing the received navigation messages into a memory built in said gps receiver; storing frequency information and time information of a high accuracy into an external clock which normally is in an operating state; and repeating a startup state and a standby state of said gps receiver within a predetermined time in response to a standby signal and a startup signal outputted from said external clock based on a setting signal transmitted from said gps receiver to said external clock and the frequency information and the time information stored in said external clock to perform position measurement of said gps receiver from said gps satellites to update the navigation messages stored in said memory.
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10. A gps position measurement method according to
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This invention relates to a navigation system for a mobile unit such as a car navigation system, and more particularly to a GPS receiver and a GPS position measurement method wherein GPS, (Global Positioning System) can be performed in a short time.
The GPS system is a position measurement system developed to allow a mobile unit such as an aircraft or a ship to determine the position on the earth or the velocity of the mobile unit on the real time basis utilizing GPS satellites which fly up in the sky. Recently, the GPS system is utilized widely in the field of the static survey for measuring the distance or the direction between different spots on the earth and the like fields in addition to the position measurement by a mobile unit. In order to utilize the GPS system, a GPS receiver for receiving radio waves radiated from GPS satellites is used.
In this manner, the GPS position measurement method requires the frequency oscillator 215 for capturing a signal from the GPS satellite 200, and in order to establish synchronism with a signal frequency of a high accuracy transmitted from the GPS satellite 200, it is required that the frequency oscillator 215 is high in accuracy. However, the oscillation frequency of the frequency oscillator 215 is fluctuated generally by a temperature or a secular change of a quartz oscillator. This fluctuation prevents easy capture of the signal from the GPS satellite 200 through the use of the frequency oscillator 215, and therefore, a scheme of a frequency search must be provided separately. Since usually the frequency search requires much time, a considerably long time is required until the current position is calculated finally.
Further, in the conventional GPS position measurement method, the time required after the signal from the GPS satellite 200 is captured until all of absolute time information included in the signal is acquired is approximately 6 seconds even upon hot starting, with which the time is minimized, and in the best conditions, but usually, a time of tens and several seconds is required. Further, since position measurement calculation is performed using the acquired absolute time information, a considerably long time is required until the current position is calculated.
Furthermore, in the conventional GPS position measurement method, when position measurement is performed again after a time longer than a fixed interval of time elapses, time for fetching a navigation message newly is required. Therefore, a considerably long time is required until the current position is calculated.
Where much time is required for GPS position measurement from such reasons as described above, for example, in a car navigation system, the current position cannot be discriminated immediately after power supply is made available. This raises a problem that the route to a destination cannot be discriminated rapidly or the current position is unsettled due to an error of the self-contained navigation and this increases time until the correct position is discriminated. Further, in an apparatus of the type wherein a GPS receiver is built in or connected to a recent portable information terminal, if the apparatus is used principally during walking of the user, since the current position cannot be measured rapidly, the user must wait at a place with the apparatus held in hand until the position measurement is completed, which is very inconvenient.
On the other hand, it is also possible to perform position measurement with the power supply normally kept on. However, this causes the apparatus to consume very much power. Where the apparatus is particularly limited in power consumption like, for example, a car navigation system or a portable navigation system, it is not preferable to normally keep the power supply on.
Also where predetermined standby/startup of a GPS receiver is repeated to intermittently receive GPS signals, in order to maintain the accuracy in frequency and time, it is necessary to reduce the interval of intermittent receptions to perform position measurement frequently, resulting in increase of the power consumption.
It is an object of the present invention to provide a GPS receiver and a GPS position measurement method wherein GPS position measurement can be performed stably and rapidly without the necessity to wait for periodical time information from a GPS satellite. It is another object of the present invention to provide a GPS receiver and a GPS position measurement method wherein power consumption is minimized also with a minimized position measurement time through the selection of an optimum time interval between intermittent receptions of GPS signals.
In order to attain the objects described above, according to an aspect of the present invention, there is provided a GPS receiver, including a GPS block for receiving a signal transmitted from a GPS satellite and performing position measurement based on the received signal to update a navigation message and for repeating a standby state for reception and a startup state thereof, and an external clock block for storing frequency information and time information of a high accuracy, the external clock block outputting a standby signal and a start signal, which are to be transmitted to the GPS block, at predetermined time intervals based on a setting signal transmitted from the GPS block and the frequency information and the time information stored in the external clock block.
The GPS receiver may further include a frequency measurement block for measuring the difference of the frequency of a frequency oscillator of the GPS block from the frequency information held in the external clock block as a frequency offset, the frequency offset being outputted from the frequency measurement block to the external clock block. Further, the external clock block may output the standby signal and the start signal, which are to be transmitted to the GPS block, at predetermined time intervals based on the accuracy of the frequency information and the time information stored in the external clock block. With the GPS receiver, further reduction in power consumption can be anticipated.
The GPS receiver may further includes a frequency measurement block for measuring a frequency offset which is a displacement of a frequency oscillator of the GPS block with reference to the frequency information held in the external clock block and outputting the measured frequency offset to the external clock block. The external clock block may control standby and startup of the GPS block based on the frequency offset outputted from the frequency measurement block. With the GPS receiver, an optimum interval of intermittent GPS receptions can be obtained based on the frequency offset of the frequency oscillator, which allows augmentation in performance and further reduction in power consumption.
According to another aspect of the present invention, there is provided a GPS receiver, including a GPS block for receiving a signal transmitted from a GPS satellite and performing position measurement based on the received signal to update a navigation message and for repeating a standby state for reception and a startup state thereof, and a radio wave clock block for storing time information of a high frequency and frequency information of a high accuracy obtained through reception of a signal transmitted from a radio wave block broadcasting station, the radio wave clock block outputting a standby signal and a start signal, which are to be transmitted to the GPS block, at predetermined time intervals based on a setting signal transmitted from the GPS block and the time information and the frequency information stored in the radio wave clock block.
The radio wave clock block may output the standby signal and the start signal, which are to be transmitted to the GPS block, at predetermined time intervals based on the accuracy of the time information and the frequency information stored in the radio wave clock block. Where the radio wave clock block is used as the external clock block in this manner, the GPS receiver is advantageous in that, when the accuracy of the time information and the frequency information held in the radio wave clock block is high, the standby state of the GPS receiver can be extended in the maximum to a valid time of a navigation message and can be further extended to further reduce the power consumption.
According to a further aspect of the present invention, there is provided a GPS position measurement method for a GPS receiver, including the steps of receiving a hierarchical navigation message from each of a plurality of GPS satellites, storing the received navigation messages into a memory built in the GPS receiver, storing frequency information and time information of a high accuracy into an external clock which normally is in an operating state, and repeating a startup state and a standby state of the GPS receiver within a predetermined time in response to a standby signal and a startup signal outputted from the external clock based on the setting signal transmitted from the GPS receiver to the external clock and the frequency information and the time information stored in the external clock to perform position measurement of the GPS receiver from the GPS satellites to update the navigation messages stored in the memory.
Also with the GPS position measurement method for a GPS receiver, the GPS measurement time can be reduced significantly, and the necessity to wait for periodical time information from a GPS satellite is eliminated. Consequently, the time required before position measurement is stabilized and reduced. Further, since an optimum GPS reception interval can be selected in accordance with a situation of the external clock, reduction of power consumption can be anticipated.
Preferably, an interval of time between startup and standby of the GPS receiver is varied based on a degree of accuracy of the frequency information or the time information held by the external clock. With the GPS position measurement method, frequency information and time information of a high accuracy and a navigation message can be held with certainty without depending upon a situation of the external clock.
It is to be noted that, for example, if the external clock is constructed for reception of a carrier from a radio wave clock broadcasting station, the accuracy of the frequency information or the time information held by the external block allows elongation of the intermittent reception interval to the maximum even if the GPS receiver does not include a real time clock (RTC) of a high accuracy.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.
A. Embodiment 1
Referring to
Meanwhile, the external clock block 2 is formed from a clock or a microcomputer having a built-in clock function which can transmit a predetermined signal in a predetermined period. The GPS block 1 sends to the external clock block 2 a setting signal indicative of a time interval after which the GPS block 1 should be started up. Upon reception of the setting signal, the external clock block 2 sets a time interval after which a start signal is to be sent to the GPS block 1. The external clock block 2 sends a start/standby signal to the GPS block 1. Upon reception of the start/standby signal, the GPS block 1 can start itself or stand by.
The frequency measurement block 3 measures a frequency offset which is an amount of displacement of the frequency of the frequency oscillator 12 of the GPS block 1 with reference to or from a frequency of a high accuracy held by the external clock block 2, and sends a value obtained by the measurement to the external clock block 2.
The digital section 20 includes a CPU (Central Processing Unit) 21 for controlling the GPS block 1, a demodulator 22 for demodulating the intermediate frequency signal, and a real time clock (RTC) 23 for producing a clock. The digital section 20 further includes a RAM 24 so that a difference between the frequency of a high accuracy of a GPS satellite and the frequency of the built-in frequency oscillator may be stored as an offset or an acquired navigation message may be stored. The digital section 20 further includes a ROM 25 which has various kinds of control information and other necessary information stored therein.
The external clock block 2 includes a CPU 31 for controlling the external clock block 2, and a real time clock (RTC) 32 connected to a quartz oscillator (XTAL) 33 and having a clock function. The external clock block 2 further includes a ROM 34 in which control information is stored, and a RAM 35 for storing time information and so forth.
The GPS receiver further includes a power supply 30 for supplying power to the GPS block 1, the external clock block 2 and other components. The power supply 30 is controlled on/off by the CPU 21 so that it should or should not supply power to the GPS block 1 thereby to allow intermittent reception (sleep reception) wherein standby/startup of the GPS block are repeated.
The frequency measurement block 3 includes an internal counter 41. The counter 41 operates with an accurate clock obtained from a reference frequency signal from the external clock block 2 to count a measurement object frequency signal from the RF section 10 of the GPS block 1 within a predetermined time produced from the clock. The frequency measurement block 3 outputs the count value of the counter 41 as frequency measurement data (frequency information) to the external clock block
The GPS block 1 to which power is supplied first executes a first time position measurement (step S101). As a result of the position measurement, the navigation message stored in the RAM 24 is updated (step S102). Then, the GPS block 1 transmits a setting signal to the external clock block 2 (step S103). The setting signal includes a valid time (usually within approximately 2 hours) of a navigation message, and a time in which the error of the clock stored by the GPS receiver remains within a fixed value or a time in which the error of the frequency oscillator 12 stored by the GPS receiver remains within a fixed value. Thereafter, the GPS block 1 receives a standby signal from the external clock block 2 (step S104). Then, if a standby signal is not received, then the position measurement is repeated, that is, the GPS block 1 repeats the processing in steps 101 to 103. If a standby signal is received, then the GPS block 1 disconnects the power supply and enters a standby mode (step S105).
Then, when that one of the times set with the setting signal which has been selected in response to the state of the external clock block 2 elapses, the GPS block 1 receives a start signal from the external clock block 2 (step S106). Thus, the GPS block 1 starts up itself (step S107). However, before a start signal is received, the GPS block 1 keeps its standby mode. At this time, if the external clock block 2 holds frequency and time information of a high accuracy, the GPS block 1 receives the frequency offset and time information as well. Then, the GPS block 1 performs position measurement again (step S101) and updates the navigation message (step S102), and then enters a standby mode similarly (steps S103 to S105). If the external clock block 2 does not store frequency and time information of a high accuracy, such information is not transmitted to the GPS block 1, and consequently, the GPS 1 performs position measurement using frequency and time information stored therein. In this manner, the GPS block 1 of the GPS receiver of the present embodiment executes intermittent position measurement in two different ways in response to a situation of the external clock block 2, that is, either executes position measurement using frequency and time information from the external clock block 2 or executes position measurement using frequency and time information stored in the inside of the GPS block 1.
On the other hand, if it is discriminated in step S122 that the frequency and time information which is held or can be acquired by the external clock block 2 is inaccurate, then the external clock block 2 updates the setting time of a timer 2 (step S129). Then, the external clock block 2 starts up the timer 2 (step S130) and transmits a standby signal to the GPS block 1 (step S131). When the time of the timer 2 updated with the setting signal elapses after the standby signal is transmitted (step S132), the external clock block 2 transmits a start signal to the GPS block 1 (step S133). In this manner, the interval of time between a standby signal and a start signal to be transmitted to the GPS block 1 is varied depending upon the accuracy of the frequency and time information which is stored or can be acquired by the external clock block 2, and also contents to be transmitted to the GPS block 1 upon transmission of a start signal can be varied.
It is to be noted that the frequency measurement block 3 uses the frequency of a high accuracy stored by the external clock block 2 as a reference to measure the frequency of the frequency oscillator 12 of the GPS block 1 or the frequency offset which is a displacement of the frequency of the frequency oscillator 12 from the frequency of the external clock block 2 and sends the measured value to the external clock block 2.
As described above, in the GPS receiver of the present embodiment, the external clock block 2 always operates, and the GPS block 1 can always store frequency and time information of a high accuracy and navigation message. Where the GPS information store such information, the time required for GPS position measurement can be reduced significantly.
Further, where the external clock block 2 always operates and the interval of time of intermittent receptions of the GPS block 1 is varied based on the accuracy of the frequency and time information which is stored or can be acquired by the external clock block 2, frequency and time information of a high accuracy and a navigation message can be stored with certainty without depending upon the situation of the external clock block 2. Further, where the external clock block 2 can store or acquire frequency and time information of a high accuracy, the valid time of the navigation message can be elongated. Therefore, the interval of time of intermittent receptions of the GPS block 1 can be increased, and consequently, reduction of the power consumption can be achieved.
In particular, as seen from
On the other hand, when no navigation message is held at a point of time when position measurement is started or when lapse of time invalidates a navigation message, further time for acquiring a navigation message is required in a GPS position measurement operation. In the GPS receiver of the present embodiment, however, since the navigation message is always updated to the latest one, acquisition of a navigation message can be omitted from position measurement. Consequently, the position measurement time can be reduced significantly.
B. Embodiment 2
The GPS receiver of the Embodiment 1 described above includes the frequency measurement block 3 so that the interval of time between intermittent receptions of GPS signals is varied in accordance with the accuracy of frequency and time information which is stored in or can be acquired by the external clock block 2. The GPS receiver of the present Embodiment 2 is a modification to but is different from the GPS receiver of the Embodiment 1 in that it uses a radio wave clock block, which makes use of a radio wave clock as an external clock, in place of the external clock block 2 to vary the interval of time of intermittent receptions of GPS signals. Thus, overlapping description of the other common components is omitted here to avoid redundancy.
Referring to
In the GPS receiver of the present embodiment, power is normally supplied to the radio wave clock block 4 so that the radio wave clock block 4 receives a signal from a radio wave clock broadcasting station to normally store time information of a high accuracy and a frequency reference of a high accuracy. The radio wave clock block 4 outputs a frequency of the carrier of 40 KHz amplified but before detected by the signal demodulation section 6 to the frequency measurement block 3. The frequency measurement block 3 thus uses the counter 41 described hereinabove to detect an error of the frequency oscillator 12 of the GPS block 1. The radio wave clock block 4 receives the error of the frequency oscillator 12 as frequency information and suitably sets a standby time based on the frequency information. Then, the radio wave clock block 4 controls standby/startup of the GPS block 1 based on the standby time so as to perform intermittent reception. The GPS block 1 starts up itself periodically under the control of the radio wave clock block 4 and updates ephemeris data necessary for position measurement calculation which are position information of GPS satellites. When the acquisition of ephemeris data is completed, the GPS block 1 enters a sleep (standby) mode. Repetitions of such startup/standby allow the GPS block 1 to normally store the latest ephemeris data.
In order to perform position measurement, the GPS block 1 receives time information and frequency information (errors) from the radio wave clock block 4 at a moment when power supply to the GPS block 1 is made available. The GPS receiver can use the information to perform such high speed position measurement as described hereinabove with reference to FIG. 7.
An interval of time between sleep receptions (intermittent reception) and average power consumption necessary to normally realize high speed position measurement where the GPS receiver of the present embodiment is used are examined here.
Where the power consumption of the GPS block 1 is represented by Wgps, the standby time by TK, and the startup time by Ton, the average power consumption Wavg can be calculated in accordance with
In the GPS receiver of the present embodiment, the sleep reception is used only for acquisition of ephemeris data, and therefore, it can be considered that the period necessary for updating the ephemeris data is equal to the interval of time between sleep receptions. Usually, it is regarded that the life of ephemeris data is approximately 2 hours. Therefore, also the updating time is considered to be 2 hours (7,200 seconds) at the maximum. Further, if it is assumed that the startup time (time for acquisition of ephemeris data) Ton is 60 seconds and the power consumption Wgps of the GPS block 1 is 580 mW, then
Thus, if it is assumed that the power consumption of the radio wave clock block 4 is 15 mW, then the total power consumption is 4.8+15=19.8 (mW). Consequently, the power consumption can be reduced significantly.
Further, with the GPS receiver of the present embodiment, even if it does not include a real time clock (RTC) of a high accuracy inside thereof, the sleep reception interval of the GPS receiver can be increased to the maximum. Also from this, the average power consumption can be suppressed low. Furthermore, since a frequency reference of a high accuracy from the radio wave clock block 4 can be utilized, even if the frequency oscillator in the GPS receiver has a great error, reliable high speed position measurement can be achieved.
While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the claims that follow.
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